The spacing of transit stops clearly affects the operating time of public transportation system, passenger travel times and vehicle emissions. A model for determining bus-stop spacing is proposed to optimize the travel time of passengers, transit operation cost, and traffic pollution in urban areas. The relationship between bus-stop spacing and vehicle operation is established from analysis of bus operation process. The amount of pollution from vehicles is calculated by putting the required time-velocity input data into mobile emission model. Finally, a bus-stop spacing model is generated aiming at minimizing passengers total travel time cost, the transit operation cost and traffic air pollution cost. A corresponding genetic algorithm is also suggested as a solution. A bus route in Wuhan is examined as an example and the results show that the optimizing method is efficient and practical.